Amino polycarboxylic compounds such as methylglycine diacetic acid (MGDA) and variants thereof e.g. NTA (nitrile triacetic acid), GDA (glutamic diacetic acid), DPA (dipicolinic acid) and IDS (imino disuccinic acid) are suitable compounds for use as builder material in detergent compositions. The use thereof is however, in most cases restricted to their use in liquid applications. This is due to the fact that these materials in solid form tend to be hygroscopic and, on storage under ambient conditions, show an unacceptably reduced flowability. Such a restricted flowability is also considered a significant drawback on production of detergent compositions.
Particles of MGDA made via conventional spray drying processes tend to be fine and dusty, have a high tendency to absorb water at ambient conditions and loose their free-flowiness. The resulting products are hygroscopic, resulting in sticky powder and even in lumps. Different routes have been developed for preparing solids from solutions of glycine-N,N-diacetic acid derivatives were these drawbacks are overcome.
U.S. Pat. No. 3,956,379 describes a process in which a concentrated slurry of NTA is spray dried at very high temperatures. This has been found to result in porous and friable products.
DD 296 680 discloses the spray-granulation of saturated solution of NTA. The example discloses a solution which is well below the saturation point of NTA. It has been found that the use of the saturated solution still results in products with very poor hygroscopicity.
In EP 845456, the crystallisation of a very concentrated composition of the glycine-N,N-diacetic acid derivatives, containing between 10 and 30% moisture is described. By this process large particles with low hygroscopicity and good flowability can be obtained. However, this process requires dedicated equipment, and the low moisture composition has been found to be very difficult to process. Consequently, such a process is quite expensive.